Ultra-low k (ULK) dielectric materials possess many properties desired in semiconductors. For instance, a layer, or film, of ultra-low k dielectric material may contain pores within the layer that help to reduce the capacitance of the semiconductor. However, the presence of these pores also necessarily decreases the strength of the film, resulting in a decrease in the film's stability during the semiconductor patterning process. The more pores present in the film, the greater the resulting damage to the ultra-low k dielectric material during processing.
There are currently a number of challenges related to the reactive ion etching (RIE) and chemical mechanical planarization (CMP) steps. Often, the top surface of the ultra-low k layer is damaged during dielectric hard mask deposition. Additionally, CMP stopping in ultra-low k layer is difficult because the ultra-low k is porous and soft, leading to a less-than-ideal CMP height uniformity. This further translates into copper interconnect height uniformity issues and increased interconnect property variability.
There are currently many advantages to using a chemical vapor deposition (CVD) or atomic layer deposition (ALD) deposited liner material in trenches formed in the ultra-low k layer. However, these deposition techniques often lead to precursor penetration deep into the ultra-low k layer, which degrades the electrical isolation between neighboring conductors.
Existing techniques for strengthening the ultra-low k layer include stuffing the pores in the layer with a substance during the subsequent processing steps. Frot et al. (Adv. Mater. 2011, 23, 2828-2832) describe filling the pores of an ultra-low k layer with an organic polymer, then subsequently removing the organic polymer, to mitigate the effects of patterning and other downstream processing steps. However, this removal of the organic material may lead to a weakening of the liner material in trenches formed in the ultra-low k layer.
Accordingly, a need exists for a process of protecting the integrity of the ultra-low k layer during fabrication without sacrificing the desired properties of the ultra-low k layer.